This invention relates to a device for spreading a substance onto a moving web of material supported by a roller, comprising a rotating bar in contact with the web material opposite to said roller, and an extrusion head having a delivery slit for supplying to said rotating bar the substance to be spread.
In the known devices of this type, the means for supplying the substance to be spread is formed by an extrusion head having a delivery slit, and the rotating bar is mounted inside the extrustion head itself within the outlet of the delivery slit. With such a construction, the spreading takes place, usually, over a width corresponding to the full extent of the rotating bar and the extrusion head. To modify the spreading width it is necessary to insert limiting members so shaped as to conform to the surface of the bar in order to provide a seal both in the delivery slit and against the bar inserted therein. This gives rise to a dangerous friction, but above all the operation of inserting such limiting members is long and difficult to carry out, especially when the work is accomplished at high temperatures, such as 200.degree.-300.degree. C., and the results are not always satisfactory. In the concerned devices it is not possible to use the customary limiting lists supported by outer list holders, which are used in the direct extrusion heads to partially occlude the delivery slit. Moreover, in devices of this kind, even in those cases in which an effective delimitation of the delivery slit could be carried out, in general it would still be necessary to mount a web support roller whose operative surface has a width exactly corresponding to the width of the web, in order to avoid any harmful direct dry friction contact between the rotating bar and the roller. Therefore, to pass from the spreading of a substance on a web of a given width to the spreading of a substance on a web of a different width it would be necessary to replace the former roller with a new roller having different characteristics, which involves the necessity of having available a set of highly expensive and bulky rollers, as well as a relatively long and difficult operation for converting the equipment.